1. Field of the Invention
The present invention relates to a method of preparing a polymerizate from a two-component organic composition, the polymerizate having a refractive index of at least 1.6, an Abbe number of at least 33 and an initial Barcol hardness of at least 1. More particularly, the present invention relates to polymerizing certain two-component organic compositions comprising at least one polycyanate reactant having at least two isocyanate and/or isothiocyanate groups, and a polyamine having at least two primary and/or secondary amine groups. The present invention also relates to polymerizates and photochromic articles.
2. Description of the Prior Art
A number of organic polymeric materials, e.g., plastics, have been developed as alternatives and replacements for glass in applications such as optical lenses, fiber optics, windows and automotive, nautical and aviation transparencies. As used herein, the term ‘glass’ is meant to refer to silica-based inorganic glass. These polymeric materials can provide advantages relative to glass, including, shatter resistance, lighter weight for a given application, ease of molding and ease of dying. Representative examples of such polymeric materials include, poly(methyl methacrylate), thermoplastic polycarbonate and poly[diethylene glycol bis(allylcarbonate)].
The refractive indices of many polymeric materials are generally lower than that of glass. For example, the refractive index of poly[diethylene glycol bis(allylcarbonate)] is about 1.50, compared to that of high index glass, which can range, for example, from 1.60 to 1.80. When fabricating lenses to correct a given degree of visual defect, e.g., a correction for myopia, the use of a polymeric material having a lower refractive index will require a thicker lens relative to a material having a higher refractive index, e.g., high index glass. When the degree of correction required is substantial, as in the case of severe myopia, a lens fabricated from a low index polymeric material can be required to be very thick. A very thick lens may negate any benefit resulting from the use of lower density lens materials relative to an equivalent degree of correction obtained from a higher refractive index glass lens. In addition, thicker optical lenses are not aesthetically desirable.
It is known that polymeric materials having refractive indices greater than 1.50 can be prepared from aromatic monomers and monomers containing halogens and/or sulfur atoms. The materials from which lenses, and in particular optical lenses, are fabricated can be categorized by their refractive indices. As those skilled in the art can appreciate, low indices typically include indices of refraction of from less than 1.50 through 1.53; middle indices comprise indices of refraction of from 1.54 through 1.57; and high indices commonly include indices of refraction of 1.58 and greater. Lenses prepared from polymeric materials having high refractive indices typically also have lower Abbe numbers (also known as nu-values). Lower Abbe numbers are indicative of an increasing level of chromatic dispersion, which is typically manifested as an optical distortion at or near the rim of the lens.
U.S. Pat. No. 5,961,889 to Jiang et al. discloses optical polymers, for use in lenses, prepared from a polythiol group-containing component, a polyisocyanate group-containing component and/or a polyfunctional vinyl group-containing component. The polymers disclosed typically had refractive indices less than 1.69 and Abbe number less than 35.
U.S. Pat. No. 5,932,681 to Herold et al. discloses an optical polymer, for use as a lens material, prepared from an isocyanate or isothiocyanate and a polythiol. The polymers disclosed have a refractive index of at least 1.57 and an Abbe number of at least 33.
U.S. Pat. No. 5,679,756 to Zhu et al. discloses an optical polymer described as a thermoplastic thiourethane-urethane copolymer prepared by reacting an aliphatic diisocyanate with a dithiol to form a thiourethane prepolymer, which is then reacted with a diisocyanate and a polyol. The polymers disclosed typically had a refractive index between 1.57 and 1.60 and Abbe number between 35 and 38.
While the optical polymers discussed above have adequate refractive indices and chromatic dispersion, they do not necessarily have the degree of impact resistance required to be suitable for use as daily wear lenses for eyeglasses.
It is accordingly desirable then to identify new polymeric materials, for example polymerizates, which can be used to prepare transparent polymerizates, particularly optical lenses that possess a combination of high refractive index and adequately high Abbe number as well as possessing the physical properties, in particular impact resistance, that are at least equivalent to and preferably better than those of lower index polymeric materials.